I wanted to add these tidbits Napi in the form of a giant rambling post (again) thanks for posting back I understand you've been dealing with a fair bit of outside responsibilities and your tank isn't going anywhere so we get to things when we can! the best is there is no hurry to act, any tank here was fine before peroxide testing even if a little greener than we'd like, taking this slow is preferable to any rush.
So I had mentioned in pm your tank to be in the top two most challenging set of treatment circumstances Id seen, those prior 3% spot testings that didn't register day 2 bleaching still have me head scratching and considering you got mutant algae lol and you had mentioned that some spot 19% did indeed burn it after a bit of delay again I couldn't figger out...
so when considering a tankwide dosage to bridge together at least some kind of activity and a possibility of helping your situation Im expecting not much to occur since we couldn't even get an emersed spot test to register. again Id say buy one more bottle from a pharmacy for 75 cents brand new just to always start on that footing.
I like to type opinionated when i feel sure about something regarding peroxide but regarding upper known tolerances for mixed fish systems I cant recall ever seeing that, the data is just not there. too many people hate the idea of even using it to study it formally like that.
Should you measure and attempt anything within some of the basic parameters I'll posit thats a tremendous helpful foot in the door even if you dont beat the algae and I have to post a loss of efficacy for the first time in this thread! You will have begun -some- kind of documentation on basic upper tolerances.
What I have read online and been told in person regarding guesstimate tolerances:
My LFS owner 20 years in the game keeps literal gallons of 35% on hand in back room to dump in his $20K+ display tanks for power outages. Serious hours-long googling will reveal this practice done in freshwater and saltwater for truly decades, maybe back to the fifties, in pet shops as a known oxygen booster in crowded tanks when support systems are down.
Theres no method to the madness, they just dump it in. Not anywhere near careful like what we do and while people are seething at us for using puny 3% lol which is laughable in comparison
My LFS's tank is mixed stony corals for sale and very profitable prices, your standard fare of sps's, acans, blue and orange linkia and sponges, huge scolymias, every darn thing you would expect from any given fish store and he personally told me several times he'd dump like half a gallon of new 35% into these 220 gallon displays when he saw fish hovering up top, naturally pooling towards the best oxygen gradients.
Same is said online in deep googling, they just dump it in.
So from that I draw nobody knows the dang true upper limit but they push the boundaries pretty hard and lose nothing they can tell from the practice. I told him incidentally he was doing a number on any diatoms or algae in the making he just laughed and said he'd never heard peroxide used for that reason, it was strictly an oxygenator for his cause. He used liberal disgusting amounts I couldn't recommend with fifty people wanting to bash me for trying to get people to use it as an algaecide lol
The very few and distant online threads from 8-10 years ago I found in deep googling on the matter said that peroxide toxicity will show up in the gills as the first receptive organ to exhibit a pre failure condition. You would mentally take note of the opercular action of your fish before treatment, and the gill coloration if viewable, to watch for changes.
As you slowly dose more and more to try and see if algae will respond, and you are using a safer 3% than I mentioned above, it seems you can start pretty darn liberal past the 1 ml/10 mark with zero expectations of fish loss truly at any known dosage. If they begin pumping gills hard, or the gills become reddened and protruding in an attempt to expel respiratory CO2/uptake systemic O2 because they can't respire, a large water change would be in order. I don't personally know an antidote for high oxygen in a tank or how to bind it other than to replace with cleaner water that is more natural in o2 content.
Im sure any residend chemists will know what to put into a reactor that has an affinity for O2, how you would prevent over scrubbing i dont know and am happy to learn. The big water change is surely a safe bet with much elbow grease involved.
Regarding water changes I say dont do any. In your size tank 3%, most likely to have no effect on your algae unless we get lucky somehow, should simply dissociate in a few days time. Id think that exporting too much of it will just lower the dissolved oxygen amounts back to pre treatment balances and offset any gain from the addition.
We are really in new territory on this one man we are going to have to proceed by feel.
Ive linked in previous pages other peroxide threads although I can't specifically recall where posters aiming to kill diatoms were bashing our 1:10 safe zone and said he had to get up to 4ml per ten gallons to beat it, still with no tank inhabitant loss and he had the usual fare of photosynthetic corals.
Im sure in any generalized dosing especially in sustained, ~4 ml:10 dosing there could be some collateral losses of some things so we'll just have to weigh that against the possibility of fixing the problem without having to deconstruct your tank and bleach the hell out of everything.
But to protect your tank again I recall you aren't short on gear...holding tanks etc, so I have to truly recommend you set up a separate tank with a few boulders of your finest and dose -that- tank with 4 mls per gallon and watch results with no fish or even corals, just see if a week of dosing 3x per that week does anything to the evil green rock lol
if you get nothing, I say don't dose your big tank and I'll hang my head in defeat after 23 pages and you'll give me regret nightmares dr sigmund couldn't repair.
